Heat exchange enhancement

ABSTRACT

A heat exchange structure includes elongated air ducts. Each air duct has a first opening and a second opening at two ends of the air duct to allow air to enter and exit the air duct, respectively. The heat exchange structure includes an exterior heat exchange surface and interior heat exchange surfaces, in which the exterior heat exchange surface is configured to receive thermal energy from heat generators that are mounted on the exterior heat exchange surface, and the exterior heat exchange surface dissipates a portion of the thermal energy received from the heat generators and transfers another portion of the thermal energy to the interior heat exchange surfaces. The interior heat exchange surfaces are in the elongated air ducts and configured to exchange thermal energy with air flowing in the air ducts, enhancing air flow in the air ducts by buoyancy of heated air.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed U.S. patentapplication Ser. No. 11/396,388, titled “Heat Exchange Enhancement” andSer. No. 11/396,364, titled “Heat Exchange Enhancement”, both of whichare incorporated herein by reference. In addition, this application is adivisional of U.S. application Ser. No. 11/396,385, filed on Mar. 31,2006. The entire contents of U.S. application Ser. No. 11/396,385 arehereby incorporated by reference.

BACKGROUND

This invention relates to heat exchange enhancement.

Electronic components often generate heat that has to be dissipated tothe surrounding environment to prevent overheating. In some examples,the heat is dissipated to ambient air. A heat sink with a larger surfacearea can be used to enhance heat dissipation. Using a fan to increaseair flow around the electronic component or the heat sink can enhanceheat dissipation. Increasing the air-solid contact area (i.e., surfacearea) may also improve the heat dissipation. Another conventional wisdomis to spread the heat to the heat sink effectively (via good conductionor convection media or both) so as to increase the difference betweenthe heat dissipation surface and the ambient air temperature, at thesame time to reduce the temperature difference between the heat sourceand the dissipation surface.

SUMMARY

In a general aspect, air-solid heat exchange can be enhanced byincreasing a heat exchange surface area of a heat conducting solidwithout blocking a natural air flow. Air ducts are provided to allowheated air to rise and exit the ducts through upper openings to carryaway heat, at the same time allowing cool air to enter the ducts fromlower openings and absorb heat from the walls of the air ducts. The airducts can reduce weak linkages in thermal conduction and heat spreading.In some examples, fins are positioned in the ducts and aligned along thedirection of air flow to increase the heat exchange surface withoutblocking the air flow. Heat exchange occurs along the length of theduct, causing hot air to continue to rise in the duct due to hot airbuoyancy, creating a pumping effect to efficiently move air through theduct without the use of fans.

In another general aspect, the quality of heat exchange between a solidstructural section and ambient air molecules can be enhanced bymodifying a surface property (for example, surface potential) of thesolid structural section, for example, by coating a thin layer ofmaterial on the solid structural section. The thin layer can be made of,for example, a ceramic material. The thin layer can have (a) spikymicro/nano structures, and/or (b) porous micro/nano structures, in whichthe spiky or porous structures (1) enhance the micro surface area, and(2) modify the solid surface potential of trapping/de-trapping(absorption & de-absorption) of air molecules for better heat transferbetween the solid surface and ambient air.

The solid structural section may include a metal structural section. Forexample, the metal structural section may include at least one ofaluminum, magnesium, titanium, zinc, and zirconium. For example, thestructural section may include an alloy of at least two of aluminum,magnesium, titanium, zinc, and zirconium. The structural section mayinclude a ceramic structural section. For example, the ceramicstructural section may include one or more of aluminum oxide, aluminumnitride, titanium oxide, titanium nitride, zirconium oxide, andzirconium nitride. In some examples, the thin layer of ceramic materialincludes at least one of aluminum carbide, aluminum nitride, aluminumoxide, magnesium carbide, magnesium nitride, magnesium oxide, siliconcarbide, silicon nitride, silicon oxide, titanium carbide, titaniumnitride, titanium oxide, zinc carbide, zinc nitride, zinc oxide,zirconium carbide, zirconium oxide, and zirconium nitride. In someexamples, the thin layer of ceramic material includes a combination ofat least two of aluminum carbide, aluminum nitride, aluminum oxide,carbon, magnesium carbide, magnesium nitride, magnesium oxide, siliconcarbide, silicon nitride, silicon oxide, titanium carbide titaniumnitride, titanium oxide, zirconium carbide, zirconium oxide, zirconiumnitride, zinc carbide, zinc nitride, and zinc oxide.

In one aspect, in general, an apparatus includes a heat exchangestructure that has elongated air ducts, each air duct having a firstopening and a second opening at two ends of the air duct to allow air toenter and exit the air duct, respectively. The heat exchange structureincludes an exterior heat exchange surface and interior heat exchangesurfaces, the exterior heat exchange surface configured to receivethermal energy from heat generators that are mounted on the exteriorheat exchange surface. The exterior heat exchange surface dissipates aportion of the thermal energy received from the heat generators andtransfers another portion of the thermal energy to the interior heatexchange surfaces. The interior heat exchange surfaces are positioned inthe elongated air ducts and configured to exchange thermal energy withair flowing in the air ducts, enhancing air flow in the air ducts bybuoyancy of heated air.

Implementations of the apparatus may include one or more of thefollowing features. The heat exchange structure includes fins that arepositioned in the air ducts for increasing the area of the secondsurfaces for exchanging thermal energy with the air flowing in the airducts. The heat exchange structure includes a metal structural sectionthat couples the first heat exchange surface to the second heat exchangesurfaces. The exterior heat exchange surface is separated from theinterior heat exchange surface by a metal wall having a thickness lessthan 5 mm. The heat exchange structure includes a structural section anda thin layer of ceramic material attached to the structural section, thethin layer of ceramic material having a thickness less than 100 μm. Theapparatus includes the heat generators. In some examples, the heatgenerators include light emitting diodes. In some examples, the heatgenerators include different portions of an electrical circuit. Theapparatus includes a plurality of mounting structures for mounting theheat generators, the mounting structures distributed on the exteriorsurface of the heat exchange structure. In some examples, the heatgenerators include electronic devices, and the mounting structuresinclude signal lines configured to be connected to the electronicdevices. The heat exchange structure defines at least one hole on a wallof the air duct to allow cool air to enter the air duct, the hole beingspaced apart from the two ends of the air duct. The apparatus includes afan to enhance airflow in the air ducts. The apparatus includes a nozzleconfigured to receive compressed air and direct the compressed air toone or more openings of the air ducts.

In another aspect, in general, an apparatus includes a heat exchangestructure that has a structural section and a thin layer of ceramicmaterial attached to a surface of the structural section, the thin layerof ceramic material having a thickness less than 100 μm. The heatexchange structure includes an elongated air duct. The heat exchangestructure has an exterior heat exchange surface and an interior heatexchange surface, the exterior heat exchange surface configured toreceive thermal energy from heat sources, the interior surface locatedin the elongated air duct and configured to exchange thermal energy withambient air flowing in the elongated air duct.

Implementations of the apparatus may include one or more of thefollowing features. The thin layer of ceramic material includes a firstsub-layer that is substantially impermeable to air molecules and asecond sub-layer that is at least partially permeable to air molecules.

In another aspect, in general, an apparatus includes a heat pipe and aheat exchange unit to exchange thermal energy with the heat pipe and toexchange thermal energy with ambient air. The heat exchange unitincludes one or more air ducts, the air flowing in the one or more airducts carrying away thermal energy from the heat exchange unit, thehousing of the heat pipe and a structural portion of the heat exchangeunit being formed from one piece of metal.

Implementations of the apparatus may include one or more of thefollowing features. The heat exchange unit includes a structural sectionand a thin layer of ceramic material attached to the structural section,the thin layer of ceramic material having a thickness less than 100 μm.

In another aspect, in general, an apparatus includes a heat pipe and aheat exchange unit that includes one or more elongated air ducts. Theheat exchange unit is configured to receive thermal energy from the heatpipe and dissipate thermal energy to ambient air flowing in the one ormore air ducts, wherein the heat pipe is aligned along an elongateddirection of the one or more air ducts.

Implementations of the apparatus may include one or more of thefollowing features. Heated vapor or liquid in the heat pipe is separatedfrom the air in the air ducts by a wall having a thickness less than 5mm. The heat exchange unit includes a structural section and a thinlayer of ceramic material attached to the structural section, the thinlayer of ceramic material having a thickness less than 100 μm.

In another aspect, in general, an apparatus includes a vehicle lamp thathas a heat exchange structure and light sources distributed on anexterior surface of the heat exchange structure. The heat exchangestructure includes a plurality of elongated air ducts. The heat exchangestructure includes an exterior heat exchange surface and interior heatexchange surfaces, in which the interior heat exchange surfaces arepositioned in the air ducts and configured to exchange thermal energywith air flowing in the air ducts. The vehicle lamp is configured todissipate thermal energy generated by the light sources through theexterior surface and interior surfaces to the air flowing in the airducts.

Implementations of the apparatus may include one or more of thefollowing features. In some examples, the vehicle lamp includes awater-tight chamber enclosing the light sources. In some examples, thevehicle lamp includes two water-tight chambers connected by a passage,one of the chambers enclosing the light sources and the other of thechambers enclosing electronic components to control the light sources,the passage allowing signal lines to pass, the signal lines connectingthe light sources to the electronic components. The heat exchangestructure includes a structural section and a thin layer of ceramicmaterial attached to the structural section, the thin layer of ceramicmaterial having a thickness less than 100 μm.

In another aspect, in general, an apparatus includes a light source thathas a plurality of light emitting diode modules, each light emittingdiode module including a heat exchange structure and light emittingdiodes distributed on the exterior surface of the heat exchangestructure. The heat exchange structure includes a plurality of elongatedair ducts. The heat exchange structure includes an exterior heatexchange surface and interior heat exchange surfaces, in which theinterior heat exchange surfaces are positioned in the air ducts andconfigured to exchange thermal energy with air flowing in the air ducts.Each light emitting diode module is configured to dissipate thermalenergy generated by the light emitting diodes through the exteriorsurface and interior surfaces to the air flowing in the air ducts.

Implementations of the apparatus may include one or more of thefollowing features. The apparatus complies with MR-16 standard. The heatexchange structure includes a structural section and a thin layer ofceramic material attached to the structural section, the thin layer ofceramic material having a thickness less than 100 μm. In some examples,the light emitting diode modules are arranged such that the lightemitting diodes of different light emitting diode modules facesubstantially the same direction. In some examples, the light emittingdiode modules are arranged such that the light emitting diodes ofdifferent light emitting diode modules face different directions.

In another aspect, in general, an apparatus includes a wall wash lighthaving a heat exchange structure and light emitting diodes distributedon the exterior surface of the heat exchange structure. The heatexchange structure includes a plurality of elongated air ducts. The heatexchange structure includes an exterior heat exchange surface andinterior heat exchange surfaces, in which the interior heat exchangesurfaces are positioned in the air ducts and configured to exchangethermal energy with air flowing in the air ducts. The wall wash light isconfigured to dissipate thermal energy generated by the light emittingdiodes through the exterior surface and interior surfaces to the airflowing in the air ducts.

Implementations of the apparatus may include one or more of thefollowing features. The wall wash light includes a water-tight chamberenclosing the light emitting diodes. The heat exchange structureincludes a structural section and a thin layer of ceramic materialattached to the structural section, the thin layer of ceramic materialhaving a thickness less than 100 μm. In some examples, the wall washlamp includes two water-tight chambers connected by a passage, one ofthe chambers enclosing the light sources and the other of the chambersenclosing electronic components to control the light sources, thepassage allowing signal lines to pass, the signal lines connecting thelight sources to the electronic components.

In another aspect, in general, a method includes receiving thermalenergy from heat generators at an exterior heat exchange surface of aheat exchange structure, in which the heat exchange structure includes aplurality of elongated air ducts, and the heat generators are positionedalong an elongated direction of the air ducts. The method includestransferring a portion of the thermal energy from the exterior heatexchange surface to interior heat exchange surfaces of the heat exchangestructure, the interior heat exchange surfaces being positioned in theair ducts, and dissipating heat from the interior heat exchange surfacesto air flowing in the air ducts to cause the heated air to rise due tobuoyancy of the heated air.

Implementations of the apparatus may include one or more of thefollowing features. The method includes using a fan to enhance air flowin the air duct. The method includes injecting compressed air into anopening of the air duct. The heat generators include electronic devices.

In another aspect, in general, a method includes transferring, through aheat pipe, thermal energy from a heat generator to a heat exchangestructure that includes a plurality of elongated air ducts, a portion ofthe heat pipe contacting the heat exchange structure being aligned alongan elongated direction of the air ducts, and transferring thermal energyfrom the heat exchange structure to ambient air flowing in the pluralityof air ducts.

Implementations of the apparatus may include one or more of thefollowing features. The method includes transferring thermal energy fromheated vapor or liquid in the heat pipe to the ambient air in the airducts through a wall having a thickness less than 5 mm.

In another aspect, in general, a method includes fabricating a heatexchange structure and a housing of a heat pipe using one piece ofmetal, in which the heat exchange structure includes a plurality of airducts and heat exchange surfaces positioned in the air ducts, and theheat exchange surfaces are configured to exchange heat with air flowingin the air ducts to enhance air flow in the air ducts due to buoyancy ofheated air.

Implementations of the apparatus may include one or more of thefollowing features. The method includes coating a surface of the heatexchange structure with a thin layer of ceramic material having athickness less than 100 μm.

In another aspect, in general, a method of operating a light sourceincludes providing electric power to a light emitting device,transferring thermal energy from the light emitting device to a firstheat exchange surface of a heat exchange structure, in which the heatexchange structure includes a plurality of elongated air ducts andsecond heat exchange surfaces positioned in the air ducts. The methodincludes transferring the thermal energy from the first heat exchangesurface to the second heat exchange surfaces, transferring thermalenergy from the second heat exchange surface to air in the air ducts,and enhancing air flow in the air duct by buoyancy of heated air thatcauses cold air to be pumped into the air ducts and hot air to be pumpedout of the air ducts.

Implementations of the apparatus may include one or more of thefollowing features. The method includes transferring thermal energy fromthe first heat exchange surface to the second heat exchange surfacesthrough a metal structural section of the heat exchange structure.

In another aspect, in general, an apparatus includes a heat exchangestructure having an exterior surface and an interior surface, and heatsources distributed on the exterior surface of the heat exchangestructure. The interior surface of the heat exchange structure definesan air duct, and the interior surface exchanges thermal energy with airflowing in the air duct.

Implementations of the apparatus may include one or more of thefollowing features. The heat exchange structure includes fins that arepositioned in the air duct for increasing a surface area for exchangingthermal energy with the air flowing in the air duct. The interiorsurface defines an elongated air duct, and the interior surface formsthe side walls of the elongated air duct. In some examples, at least oneof a portion of the interior surface and a portion of the exteriorsurface includes a metal surface.

The heat exchange structure includes a structural section and a thinlayer of material attached to the structural section, the thin layer ofmaterial having a thickness less than 100 μm. At least one of a portionof the interior surface and a portion of the exterior surface of theheat exchange structure includes a surface of the thin layer ofmaterial. The thin layer of material includes a ceramic material. Theceramic material may include at least one of aluminum oxide, aluminumnitride, aluminum carbide, beryllium oxide, beryllium nitride, berylliumcarbide, lithium oxide, lithium nitride, lithium carbide, magnesiumoxide, magnesium nitride, magnesium carbide, silicon carbide, siliconoxide, silicon nitride, titanium carbide, titanium oxide, titaniumnitride, zinc carbide, zinc oxide, zinc nitride, zirconium carbide,zirconium nitride, and zirconium oxide. In some examples, the ceramicmaterial includes a combination of at least two of aluminum oxide,aluminum nitride, aluminum carbide, beryllium oxide, beryllium nitride,beryllium carbide, lithium oxide, lithium nitride, lithium carbide,magnesium oxide, magnesium nitride, magnesium carbide, silicon carbide,silicon oxide, silicon nitride, titanium carbide, titanium oxide,titanium nitride, zinc carbide, zinc oxide, zinc nitride, zirconiumcarbide, zirconium nitride, and zirconium oxide.

The interior surface includes a substantially isothermal surface. Theair flow in the air duct is enhanced by buoyancy of hot air that causescool air to be pumped into a first opening of the air duct and hot airto be pumped out of a second opening of the air duct. Both the exteriorsurface and the interior surface are heat dissipating surfaces. The heatsources include light emitting diodes. The heat exchange structuredefines at least one hole on a wall of the air duct to allow cool air toenter the air duct, the hole being spaced apart from two ends of the airduct. The hole has a size and shape that is configured and designed toallow cool air to enter the air duct to regulate a speed of air flow inthe air duct to achieve an optimal heat exchange rate. The holes alsoallow hot air to exit the air duct when the air duct is positionedhorizontally.

In another aspect, in general, an apparatus includes a heat exchangestructure having a structural section and a thin layer of ceramicmaterial attached to at least a portion of a surface of the structuralsection, the thin layer of ceramic material having a thickness less than100 μm. The heat exchange structure has an exterior surface and aninterior surface, the interior surface defining an elongated air duct,the interior surface exchanging thermal energy with air flowing in theair duct. The apparatus includes heat sources distributed on theexterior surface of the heat exchange structure.

Implementations of the apparatus may include one or more of thefollowing features. The thin layer of ceramic material includes a firstsub-layer and a second sub-layer, in which the first sub-layer includesa solid layer that is impermeable to air molecules, and the secondsub-layer has a porous structure that is at least partially permeable toair molecules.

In another aspect, in general, an apparatus includes a heat exchangestructure having a first heat exchange surface and a second heatexchange surface, in which a portion of the first heat exchange surfaceexchanges thermal energy with a heat source, and the second heatexchange surface defines one or more air ducts. Air flowing in the oneor more air ducts carries thermal energy away from the second heatexchange surface.

Implementations of the apparatus may include one or more of thefollowing features. The heat exchange structure includes heat exchangefins positioned in at least one of the one or more air ducts. The heatexchange fins are aligned along a direction parallel to an elongateddirection of the one or more air ducts. The apparatus includes an activedevice to enhance air flow in the air duct. The active device includes afan. The active device includes at least one of an air compressor and acontainer containing compressed air for generating compressed air thatis injected into at least one opening of the one or more air ducts. Theactive device regulates the air flow in the air duct to achieve anoptimal heat exchange rate. The heat exchange structure includes a metalor a metal alloy. At least a portion of the second heat exchange surfaceis coated with a thin layer of material having a thickness less than 100microns. The thin layer of material increases a heat exchangecoefficient between the heat exchange structure and ambient air.

The thin layer of material includes a ceramic material. The ceramicmaterial may include at least one of aluminum oxide, aluminum nitride,aluminum carbide, beryllium oxide, beryllium nitride, beryllium carbide,lithium oxide, lithium nitride, lithium carbide, magnesium oxide,magnesium nitride, magnesium carbide, silicon carbide, silicon oxide,silicon nitride, titanium carbide, titanium oxide, titanium nitride,zinc carbide, zinc oxide, zinc nitride, zirconium carbide, zirconiumnitride, and zirconium oxide. In some examples, the ceramic materialincludes a combination of at least two of aluminum oxide, aluminumnitride, aluminum carbide, beryllium oxide, beryllium nitride, berylliumcarbide, lithium oxide, lithium nitride, lithium carbide, magnesiumoxide, magnesium nitride, magnesium carbide, silicon carbide, siliconoxide, silicon nitride, titanium carbide, titanium oxide, titaniumnitride, zinc carbide, zinc oxide, zinc nitride, zirconium carbide,zirconium nitride, and zirconium oxide.

The apparatus includes the heat source coupled to a portion of the firstheat exchange surface. The heat source includes one or more lightemitting diodes. The heat source includes a distributed heat source, thedistributed heat source being distributed on the first heat exchangesurface. The second heat exchange surface includes a substantiallyisothermal surface. An air flow in the air duct is facilitated bybuoyancy of hot air that pumps cool air into a first opening of the airduct and blows hot air out of a second opening of the air duct.

In another aspect, in general, an apparatus includes a heat pipe and aheat exchange unit to exchange thermal energy with the heat pipe and toexchange thermal energy with ambient air. The heat exchange unit definesone or more air ducts, and the air flowing in the one or more air ductscarries away thermal energy from the heat exchange unit.

Implementations of the apparatus may include one or more of thefollowing features. The heat pipe includes a housing that encloses aliquid. The housing of the heat pipe and the heat exchange unit are madeof the same material. The housing of the heat pipe and the heat exchangeunit are formed from one piece of metal. The heat exchange unit isconstructed and designed to transfer heat from the heat source to theambient air without use of a fan. The apparatus includes one or morelight emitting diodes that are coupled to the heat pipe and dissipateheat to the heat pipe. An air flow in the air duct is facilitated bybuoyancy of hot air that pumps cool air into a first opening of the airduct and blows hot air out of a second opening of the air duct.

In another aspect, in general, a vehicle lamp includes a heat exchangestructure having an exterior surface and an interior surface, theinterior surface defining an elongated air duct, and light sourcesdistributed on the exterior surface of the heat exchange structure.

Implementations of the apparatus may include one or more of thefollowing features. The light sources include light emitting diodes. Theair duct is oriented substantially vertically when the vehicle lamp isinstalled on a vehicle. The vehicle lamp includes an air scoop to directair towards an opening of the air duct. In some examples, the vehiclelamp may include one water-tight chamber enclosing the light sources andelectronic components for controlling the light sources. In someexamples, the vehicle lamp may include two water-tight chambers: a firstwater-tight chamber enclosing the light sources and a second water-tightchamber enclosing electronic components to control the light sources.The heat exchange structure defines a passage to allow signal lines topass, the signal lines connecting the light sources to the electroniccomponents. The passage only connects the first and second water-tightchambers, and is not connected to ambient air.

In another aspect, in general, a vehicle includes a body, wheelsrotatably coupled to the vehicle body, an engine for driving the wheels,and a head lamp for illuminating areas in front of the vehicle. The headlamp includes light emitting diodes and a heat exchange structure havingan exterior heat exchange surface and an interior heat exchange surface.The light emitting diodes are coupled to the exterior heat exchangesurface, and the interior heat exchange surface defines an elongated airduct in which air flowing in the elongated air duct carries heat awayfrom the interior heat exchange surface.

Implementations of the apparatus may include one or more of thefollowing features. The heat exchange structure includes a compositesubstrate that includes a substrate and a thin layer of material havinga thickness less than 100 microns. The thin layer of material includes aceramic material.

In another aspect, in general, a light source includes a heat exchangestructure having an exterior surface and interior surfaces, the interiorsurfaces defining air ducts that are spaced apart along a firstdirection parallel to the exterior surface, and an array of lightemitting devices that coupled to the exterior surface of the heatexchange structure.

Implementations of the apparatus may include one or more of thefollowing features. The air ducts are elongated along a second directionparallel to the exterior surface. The light sources include lightemitting diodes.

In another aspect, in general, a method includes receiving thermalenergy from one or more heat sources, transferring the thermal energyfrom a first heat exchange surface of a heat exchange structure to asecond heat exchange surface of the heat exchange structure, the secondheat exchange surface defining an air duct, and exchanging thermalenergy between the second heat exchange surface and air flowing in theair duct.

Implementations of the apparatus may include one or more of thefollowing features. Exchanging thermal energy between the heat exchangesurface and the air in the air duct includes dissipating heat from oneor more fins in the air duct to the air in the air duct. The methodincludes using a fan to enhance air flow in the air duct. The methodincludes injecting compressed air into an opening of the air duct. Themethod includes transferring thermal energy from the one or more heatsources to the first heat exchange surface through a heat pipe.

In another aspect, in general, a method includes fabricating a heatexchange structure and a housing of a heat pipe using one piece ofmetal, the heat exchange structure defining one or more air ducts.

Implementations of the apparatus may include one or more of thefollowing features. The method includes coating at least a portion ofthe surface of the heat exchange structure with a thin layer of materialhaving a thickness less than 100 μm. The thin layer of material includesa ceramic material. Fabricating the heat exchange structure and thehousing includes using an extrusion process to form the heat exchangestructure and the housing.

In another aspect, in general, a method includes positioning heatsources on a first surface of a heat exchange structure in a distributedmanner to cause a second surface of the heat exchange structure to havea less temperature gradient than if the heat sources were concentratedat a location on the first surface, in which the second surface definesan air duct.

Implementations of the apparatus may include one or more of thefollowing features. Positioning the heat sources includes distributingthe heat sources on the first surface to cause the second surface to besubstantially isothermal. The method includes dissipating heat from thesecond surface to air flowing in the air duct. Positioning heat sourceson the first surface include positioning electronic devices on the firstsurface. Positioning heat sources on the first surface of the heatexchange structure include attaching a heat pipe to the heat exchangestructure, the heat sources includes the different portions of the heatpipe.

In another aspect, in general, a method of operating a light sourceincludes providing electric power to a light emitting device,transferring thermal energy from the light emitting device to a firstheat exchange surface of a heat exchange structure, transferring thethermal energy from the first heat exchange surface to a second heatexchange surface of the heat exchange structure, the second surfacedefining an air duct, and transferring thermal energy from the secondheat exchange surface to air flowing in the air duct.

Implementations of the apparatus may include one or more of thefollowing features. Transferring the thermal energy from the first heatexchange surface to the second heat exchange surface includes causingthe second heat exchange surface to become substantially isothermal. Themethod includes enhancing air flow in the air duct by buoyancy of hotair that causes cool air to be pumped into a first opening of the airduct and hot air to be pumped out of a second opening of the air duct.

Advantages of the heat exchange structure can include one or more of thefollowing. When the surface properties of the heat exchange structureare modified to increase the micro- and/or nano-structures of the heatdissipation surface, the efficiency of heat exchange between the heatexchange structure and ambient air can be increased without the use offans and without increasing the overall volume of the heat exchangestructure. The surface properties of the heat exchange structure can bemodified to enhance the solid surface absorption and de-absorptionpotential for air molecules. The action of absorption and de-absorptioncan create micro turbulences on the surfaces of the heat exchangestructure, which can enhance the heat exchange rate. The air ducts cangenerate an air pumping effect to move air faster for more efficientheat exchange without the use of fans and without increasing the overallvolume of the heat exchange structure.

A number of patent applications have been incorporated by reference. Incase of conflict with the references incorporated by reference, thepresent specification, including definitions, will control.

Other features and advantages of the invention are apparent from thefollowing description, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1-4 show heat exchange structures.

FIG. 5A shows a metal structural section and a heat exchange structure.

FIG. 5B is a cross-sectional diagram of a metal structural section and athin ceramic layer.

FIG. 5C is a diagram of structures at a surface of the thin ceramiclayer of FIG. 5B.

FIG. 5D is a photograph of a cross-sectional diagram of a metalstructural section and a thin ceramic layer.

FIGS. 6-7 are graphs.

FIG. 8 shows a heat exchange structure having a ceramic structuralsection.

FIG. 9 is a diagram of an air duct.

FIG. 10A is an exploded diagram of an automobile fog lamp.

FIG. 10B shows electronic circuit devices attached to a heat exchangestructure of the fog lamp of FIG. 10A.

FIG. 10C is an assembled view of the lamp of FIG. 10A.

FIG. 11A is an exploded diagram of a front-emitting light source.

FIG. 11B shows LED modules of FIG. 11A.

FIG. 11C is an assembled view of the light source of FIG. 11A.

FIG. 12A is an exploded diagram of a side-emitting light source.

FIG. 12B is an assembled view of the light source of FIG. 12A

FIG. 13A is an exploded diagram of a wall wash light.

FIG. 13B shows electrical circuit devices on a heat exchange structure.

FIG. 13C is an assembled view of the wall wash light of FIG. 13A

DESCRIPTION Heat Exchange Structure Having Air Ducts

Referring to FIG. 1, a solid heat exchange structure 100 removes heatfrom heat sources 112 with a high efficiency. The heat exchangestructure 100 is made of a material having a high heat conductioncoefficient and functions as a heat conduit to transfer heat from theheat sources 112 to ambient air or other gases. The heat exchangestructure 100 has exterior heat exchange surfaces 118 that can dissipateheat to the ambient air. The heat exchange structure 100 also hasinterior heat exchange surfaces 120 positioned in elongated air ducts102.

In this description, an “interior surface” of a device refers to asurface interior to an overall structure of the device. A heat sourcecan be a heat generator, for example, active electronic devices such aslight emitting diodes (LEDs) that generate heat. A heat source can alsobe a portion of a heat pipe that transfers heat from a heat generator toa heat dissipation surface.

The interior heat exchange surfaces 120 can dissipate heat to the airflowing in the air ducts 102. Due to an air pumping effect describedbelow, airflow in the air duct across the interior heat exchangesurfaces 120 is greater than airflow across the exterior heat exchangesurfaces 118. The air ducts 102 enhance heat dissipation withoutincreasing the overall volume of the structure 100.

The air ducts 102 each have two openings. In this example, where the airducts are aligned substantially vertically, the first openings of an airduct is a lower openings 106, and the second opening is an upper opening110. Cold air 104 enters the air ducts 102 from the lower openings 106,and hot air 108 exits the air ducts 102 from the upper openings 110.

In some examples, the heat sources 112 are distributed on the exteriorsurface 118 along a direction 124 parallel to an elongated direction(lengthwise direction) of the air ducts 102 so as to maintain theinterior heat exchange surfaces 120 in a substantially isothermal state,i.e., common temperature. The temperature difference between differentportions of the heat exchange surfaces 120 is smaller than thetemperature difference between the heat exchange surfaces 120 and theambient air. As the air rises inside the air ducts 102 due to hot airbuoyancy, the air is successively heated by the interior heat exchangesurfaces 120, creating an air pumping effect to cause the air tocontinue to rise.

In examples in which the heat sources 112 are concentrated near thelower portion of the exterior heat exchange surface 118, the lowerportion of the interior heat exchange surfaces 120 has a highertemperature, and the upper portion of the interior heat exchangesurfaces 120 has a lower temperature. The air heated by the lowerportion of the interior heat exchange surfaces 120 may become cooler asthe air rises within the air ducts 102, causing the air to flow moreslowly due to reduced air buoyancy.

The area of the heat exchange surfaces 120 in the air ducts 102 can beincreased by using fins 114 that protrude into the air ducts 102. Thefins 114 extend in a direction 124 parallel to the elongated directionof the air ducts 102 so that the fins 114 do not block the air flow.

In some examples, the heat exchange structure 100, including the finsand the walls that define the air ducts 102, are formed, for example byextrusion, from a single piece of metal (for example, aluminum) having ahigh thermal conductivity. By using a single piece of metal, there is nothermal interface within the solid heat exchange structure 100, thusimproving transfer of heat from a surface of the heat exchange structure110 that receives heat from the heat sources 112 to another surface ofthe heat exchange structure 110 that dissipates heat to the air.

Electronic circuitry 116 can be mounted on the heat exchange structure100, in which the circuitry 116 interacts with the heat sources 112.Examples of the heat sources 112 include light emitting diodes (LEDs)and microprocessors.

Portions 122 of the heat exchange structure 100 between the air ducts102 can be solid. The portions 122 alternatively can be hollow andinclude fluid (for example, distilled water), so that the portions 122function as heat pipes. In examples where the heat sources 112 are notdistributed along the direction 124, such as when there is only one heatsource, or where the heat sources are spaced apart along a direction atan angle to the direction 124, the heat pipes can be used to distributethe heat along the direction 124 and heat the air in the air ducts 102successively as the air passes through the air ducts 102.

FIG. 2 shows another view of a portion of the heat exchange structure100, including the interior heat exchange surface 120, which defines thewalls of the air ducts 102, and fins 114 that protrude into the airducts 102.

FIG. 3 shows an example of a heat exchange structure 130 that uses aheat pipe 132 to transfer heat from heat sources 112 to heat exchangeunits 134. The heat pipe 132 has a lower portion 136 that contacts theheat sources 112 and an upper portion 138 that contacts the heatexchange units 134. The upper portion 138 of the heat pipe 132 can belocated between two heat exchange units 134. The heat exchange units 134define air ducts 102 to enhance the flow of air over heat exchangesurfaces, similar to the air ducts 102 of the structure 100 in FIG. 1.

The heat pipe 132 includes a fluid (for example, distilled water), anduses evaporative cooling to transfer thermal energy from the lowerportion 136 to the upper portion 138 by the evaporation and condensationof the fluid. The upper portion 138 functions as a distributed heatsource to the heat exchange units 134 to maintain the walls of the airducts 102 at substantially the same temperature. The walls of the airducts 102 heats the air inside the air ducts 102 successively, creatingan air pumping effect to cause heated air to rise faster in the airducts 102.

In some examples, the heat pipe 132 and the heat exchange units 134 arefabricated by, for example, an extrusion process in which the heat pipe132 and the heat exchange units 134 are formed together from one pieceof metal (for example, aluminum) having a high thermal conductivity. Insome examples, the heat pipe 132 can be formed by, for example, welding(sealing) the ends of some of the heat exchange units 134. By using asingle piece of metal, there is no thermal barrier within the solid heatexchange structure 130, so that heat conduction within the heat exchangestructure 130 is better, and the transfer of heat from the heat sources112 to the solid-air heat exchange surfaces is more efficient, ascompared to a structure in which the heat pipe 132 and the heat exchangeunits 134 are separate pieces that are attached together.

An advantage of the heat exchange structure 130 is that the upperportion of the heat pipe is aligned substantially parallel to theelongated direction of the air ducts 102. Heated air rises within theair ducts, such that cold air enters the air ducts from below and hotair exits the air ducts from above. Heated vapor rises inside the heatpipe, and condensed liquid flows downward. This allows the transfer ofthermal energy from the heat sources 112 to the air inside the air ducts102 to be more efficient, as compared to examples where heat pipestransfer heat to heat dissipating fins, in which the heat pipes arealigned along a direction perpendicular to the direction of air flowbetween adjacent heat dissipating fins.

FIG. 4 shows an example of a heat exchange structure 140 that uses aheat pipe 142 to transfer heat from heat sources 112 to heat exchangeunits 144. The heat pipe 142 has a lower portion 146 that contacts heatsources 112 and upper portions 148 that are sandwiched between heatexchange units 144. The heat exchange units 144 define air ducts 102 toenhance the flow of air over the heat exchange surfaces, similar to theair ducts 102 of the structure 100 in FIG. 1. Openings 150 are providedat the sides near the bottom of the heat exchange units 144 to allowcool air to flow into the air ducts 102. The heat exchange structure 140has more heat exchange units 144 and can dissipate heat at a faster rate(as compared to the heat exchange structure 100 or 130).

Commercially available thermal simulation software, such as FLOTHERM,from Flomerics Group PLC, Hampton Court, United Kingdom, can be used tooptimize the size of the heat pipe 138, the size and number of the heatexchange units 134, and locations of the inlet and outlet openings ofthe air ducts 102. These parameters depend in part on the geometry ofthe air ducts 102, the material of the heat exchange structure 140, andthe normal operating temperature of the heat sources 112.

In some examples, the heat pipe 142 and the heat exchanging units 144are fabricated by an extrusion process in which the heat pipe 132 andthe heat exchange units 134 are formed from one piece of metal (forexample, aluminum) having a high thermal conductivity. By using a singlepiece of metal, there is no thermal barrier within the solid heatexchange structure 140, so that heat conduction within the heat exchangestructure 140 is better, and the transfer of heat from the heat sources112 to the solid-air heat exchange surfaces is more efficient.

As an alternative to using heat pumping by natural buoyancy of heatedair, compressed air can be injected into the lower openings of the airducts 102 of the heat exchange structures 100, 130, or 140. Thecompressed air absorbs heat as it expands and decompresses to roompressure, further enhancing removal of heat from the solid-air heatexchange surface 120 of the solid heat exchange structure 100, 130, or140. A compressor for compressing air can be located at a distance fromthe heat exchange structure 100, 130, or 140, and a pipe can convey thecompressed air to the lower openings of the air ducts 102. Thecompressed air can also be provided by a compressed air container.

The heat exchange structures described above, such as 100 (FIG. 1), 130(FIG. 3), and 140 (FIG. 4), can be used with or without a fan. Note thata higher fan speed does not necessarily result in better heat transfer.For a given configuration of the heat exchange structure 100, 130, or140, when used with a fan, the speed of the fan can be adjusted toobtain an optimal heat exchange rate.

For the heat exchange structures 100, 130, and 140, when the air duct102 is long and the rate of heat exchange between the air duct walls andthe air inside the air duct is large, the pressure inside the air duct(especially near the upper opening 110) is lower than the ambientatmospheric pressure. The flow of hot air out of the upper opening 110may be impeded by the higher ambient atmospheric pressure, reducing theefficiency of heat exchange between the air and the air duct walls.

In some examples, the heat exchange structure 100 includes holes on theside walls of the air ducts 102 to allow cold air to enter mid-sectionsof the air ducts and intermix with the hot air. This reduces thetemperature of the hot air in the air ducts 102, reducing the pressuredifference between the hot air exiting the upper opening 110 and theambient air outside of the upper opening 110, and may result in betterheat dissipation.

In some examples, the heat exchange structure (e.g., 100) can beoriented such that the air ducts 102 are positioned horizontally so thatthe openings 106 and 110 are of the same height. In such cases, theholes can facilitate air flow in the air ducts. A horizontallypositioned air duct can have a heat exchange efficiency about, forexample, 50% to 90% of the heat exchange efficiency of the same air ductpositioned vertically, depending on the duct size and the conductivityof the heat exchange structure.

In the examples of FIGS. 1 and 3, holes can be drilled on the heatexchange surface 118 of the heat exchange structures 100 and 130,respectively. In the example of FIG. 4, the heat exchange unit 144 canbe made longer than the heat pipes 148, so that holes can be drilled inthe outer walls of the heat exchange unit 144 that extend beyond theheat pipes 148.

The size, number, and location of the holes depend in part on thegeometry of the air ducts, the material of the heat exchange structure,and the normal operating temperature of the heat sources 112.Commercially available thermal simulation software, such as FLOTHERM,can be used to determine the size, number, and location of the holes.

Modification of Surface Properties

The solid-air heat exchange surfaces of the heat exchange structure 100,130, or 140 include the surfaces 120 and the surfaces of the fins 114facing the air ducts 102, and the exterior surfaces 118. In someexamples, the solid-air heat exchange surfaces can be coated with a thinlayer of material, such as a ceramic material, to modify the surfaceproperties of the solid heat exchange structure to enhance heat exchangewith the air molecules. For example, the thickness of the coated ceramicmaterial can be less than 100 μm.

The modification of the surface property is also applicable in otherstructures where good, solid-air thermal conductivity is desirable.

The thin layer of material can include either or both of (a) a spikymicro- and/or nano-structure, and (b) a porous micro- and/ornano-structure. By applying the thin layer of material, the surfaceenergy of the solid structure can be modified to (1) enhance the microsurface area while keeping the macroscopic surface dimension, and (2)modify the solid surface potential of trapping and de-trapping(absorption and de-absorption) of air molecules for better heattransfer. The thin layer of material coated on the heat exchangestructure not only increases the effective surface heat exchange area,but also changes the way that air molecules interact with the surface ofthe heat exchange structure, thereby enhancing the ability of the heatexchange structure to exchange heat with the ambient air.

Referring to FIG. 5A, a heat exchange structure 164 is constructed byattaching thin ceramic layers 162 to a metal structural section 160. Themetal structural section 160 is rigid and defines the structure of theheat exchange structure 164. The thin ceramic layers 162 modify thesurface properties of the metal structural section 160.

The thin ceramic layers 162 can be coated onto the metal structuralsection 160 by a micro-arc-oxidation plating process, in which certainchemicals used to form the thin ceramic layers 162 are mixed into anelectrolyte used in the plating process. The ingredients of thechemicals include one or more of aluminum oxide, aluminum nitride,aluminum carbide, beryllium oxide, beryllium nitride, beryllium carbide,boron oxide, hafnium oxide, lithium oxide, lithium nitride, lithiumcarbide, magnesium oxide, magnesium nitride, magnesium carbide, siliconoxide, silicon nitride, silicon carbide, titanium oxide, titaniumnitride, titanium carbide, zirconium oxide, zirconium carbide, zirconiumnitride, zinc oxide, zinc carbide, and zinc nitride. The ingredients mayalso include carbon.

The metal structural section 160 can be made of a single metal, such asaluminum, beryllium, lithium, magnesium, titanium, zirconium, or zinc.The metal structural section 160 can also be made of an alloy, such asan alloy of at least two of aluminum, magnesium, titanium, zirconium,and zinc.

The thin layer of ceramic material can be made of, for example, aluminumoxide, aluminum nitride, aluminum carbide, beryllium carbide, berylliumoxide, beryllium nitride, boron oxide, carbon, hafnium carbide, hafniumoxide, lithium carbide, lithium nitride, lithium oxide, magnesiumcarbide, magnesium oxide, magnesium nitride, silicon carbide, siliconoxide, silicon nitride, titanium carbide, titanium oxide, titaniumnitride, zirconium oxide, zirconium carbide, zirconium nitride, zinccarbide, zinc oxide, or zinc nitride. The thin layer of ceramic materialcan also be made of a combination of two, three, or more of, forexample, aluminum carbide, aluminum oxide, aluminum nitride, berylliumcarbide, beryllium oxide, beryllium nitride, boron oxide, carbon,hafnium carbide, hafnium oxide, lithium carbide, lithium nitride,lithium oxide, magnesium carbide, magnesium oxide, magnesium nitride,silicon carbide, silicon oxide, silicon nitride, titanium carbide,titanium oxide, titanium nitride, zinc carbide, zinc oxide, zincnitride, zirconium oxide, zirconium carbide, and zirconium nitride.

Referring to FIG. 5B, in some examples, the plating process causes athin ceramic layer 162 having porous and spiky structures to form on themetal structural section 160. In some examples, the thin ceramic layer162 includes a first sub-layer 166 and a second sub-layer 168. The firstsub-layer 166 is a solid ceramic thin layer that is impermeable to airmolecules, and can have a thickness less than 10 microns. In some cases,the first sub-layer 166 is less than 5 microns. The second sub-layer 168is a sponge-like porous layer that is partially permeable to airmolecules, and has a thickness less than 100 microns. In some examples,the second sub-layer 168 is less than 25 microns. The second sub-layer168 has porous structures with voids having diameters of a few microns.The shape of the voids can be irregular. The walls of the porousstructures can range from submicron to microns.

Each of the sub-layers 166 and 168 can be made of a ceramic material ora ceramic composite. For example, the sub-layers 166 and 168 can be madeof ceramic composites that include carbon, silicon oxide, aluminumoxide, boron oxide, titanium nitride, and hafnium nitride.

FIG. 5C shows an enlargement of a surface 169 of the second sub-layer162. The surface 169 has spiky structures 167 that have heights lessthan 250 nanometers and diameters less than 1 micron (ranging from a fewnanometers to several hundred nanometers).

FIG. 5D is a cross sectional photograph of the metal layer 164 and theceramic thin layer 162. In this example, the thickness of the thin layer162 is about 78 microns. The first sub-layer 166 can be seen at theinterface between the lower, darker portion and the upper, brighterportion of the photograph. The spiky structures 167 are too small to beseen in the photograph.

The heat exchange structure 164 is a good electric insulator (due to thethin layer of ceramic at the surface), as well as a good thermalconductor. Because of the good electric insulation property, the heatexchange structure 164 can be used as a printed circuit board. Forexample, a resin coated copper foil can be adhered to the surface of theheat exchange structure 164 and etched to form signal lines and bondingpads. Electronic circuits and semiconductor devices can be soldered tothe bonding pads. Portions of the heat exchange structure 164 that arenot covered by the copper signal lines are exposed to ambient air andprovide better heat dissipation (as compared to a circuit board made ofa dielectric material).

The thin ceramic layer 162 can increase the effective surface heatexchange area and change the way that air molecules interact with thesurface of the solid structure. The ceramic layer can have spiky micro-and/or nano-structures, and/or porous micro- and/or nano-structures. Theporous structures allow air to permeate the thin layer. The spiky and/orporous structures can enhance the micro surface area, and modify thesolid surface potential of trapping and de-trapping (absorption andde-absorption) of air molecules for better heat transfer between theheat exchange solid surface and ambient air.

Instead of coating the metal structural section 160 with a thin layer ofceramic material, the metal structural section 160 can also be coatedwith a ceramic composite material, which includes two or more ceramicmaterials, also using the micro-arc-oxidation plating process, using amodified electrolyte having suspended nano-ceramic materials in theelectrolyte.

Without being bound by its accuracy, below is a theory of why modifyingthe surface potential of the solid-air heat exchange surface may enhanceheat transfer from the solid surface to air molecules.

Thermal energy in a solid is manifested as vibration of molecules in thesolid, and thermal energy in a gas is manifested as kinetic energy ofthe gas molecules. When gas molecules come into contact with themolecules at the surface of the solid, energy may be transferred fromthe solid molecules to the gas molecules, so that the solid moleculeshave reduced vibrations, and the gas molecules have increased kineticenergy. The transfer of thermal energy from molecules of the solid tothe gas molecules can be enhanced by increasing the interaction betweensolid and gas molecules.

FIG. 6 shows a curve 170 that represents a relationship between thesurface potential of a solid and the distance from the surface of thesolid. At distances far away from the surface of the solid (for example,more than one micron), the surface potential is near zero. At locations(such as at a point P) closer to the solid surface, the surfacepotential is negative. When the distance to the solid surface is aparticular value Zm (such as at a point Q), the surface potential has aminimum value D. At locations closer than Zm (such as at a point R), thesurface potential increases and becomes positive. For metals, such asaluminum alloys, the value of Zm can be in the range of 10 nm to 100 nm.

The curve 170 indicates that, at the vicinity (e.g., within 100 nm) of asolid surface, there is a “potential well” that can “trap” air moleculeshaving lower kinetic energy. For air molecules that are in the vicinityof the solid surface and have kinetic energy that are less than D, theair molecules may be trapped near the surface of the solid because theirkinetic energy are not sufficient to overcome the negative surfacepotential of the solid. The trapped air molecules are more denselypacked in the potential well, as compared to the air molecules atfarther distances (e.g., more than 1 micron). The more densely packedair molecules move within the potential well and have higherprobabilities of colliding with the molecules of the solid, causingenergy to transfer from the solid molecules to the air molecules. If theair molecules have kinetic energy increased to a level sufficient toovercome the negative surface potential, the air molecules may be“de-trapped” and escape the potential well, carrying away thermal energyfrom the solid.

FIG. 7 shows the Maxwell-Boltzmann energy distribution of a given numberof particles at different temperatures. Curves 180, 182, and 184represent the energy distributions of particles at temperatures T1, T2,and T3, respectively, in which T1<T2<T3. The sum of shaded portions 186,188, and 190 below the curve 180 represent the portion of particleshaving energy equal to or less than E1 at temperature T1. Similarly, thesum of shaded portions 188 and 190 below the curve 182 represent theportion of particles having energy equal to or less than E1 attemperature T2, and the shaded portion 190 below the curve 184 representthe portion of particles having energy equal to or less than E1 attemperature T3. The shaded portions 186, 188, and 190 indicate that, asthe temperature increases, the percentages of particles having energyequal to or less than E1 decreases.

The kinetic energy of a particle increases in proportion to the squareof the particle's speed. FIG. 7 indicates that, as the temperatureincreases, the percentages of particles having kinetic energy less thana certain value decreases. Consider a situation where air moleculeshaving a temperature of T1 come into contact with a hot solid surfaceand are heated by the hot solid surface. Initially, a larger percentageof the cooler air molecules have lower kinetic energy that can betrapped in the potential well. After energy is transferred from thesolid to the air molecules (for example, by phonon vibration), thetemperature of the air molecules increases to T3. A portion of the airmolecules (represented by the shaded portions 186 and 188) in thepotential well gain sufficient energy to leave the potential well,carrying away energy from the solid. By continuously providing coolerair molecules to replenish the heated air molecules that escaped fromthe potential well, thermal energy can be continuously transferred fromthe solid surface to the air molecules.

Interaction between the solid and air molecules can be enhanced bymodifying the surface potential of the solid, for example, by causingthe potential well to become “deeper” (i.e., that the lowest potentiallevel D becomes more negative), or altering the shape of the potentialcurve, so that more air molecules can be trapped in the potential well.The surface potential can be modified to increase the “trapping rate” oflow energy air molecules to increase the density of solid-air moleculecontacts, and to increase the “escaping rate” for high energy airmolecules that carry energy away from the solid.

Referring back to FIG. 5A, coating the thin ceramic layer 162 on themetal structural section 160 has the effect of lowering the surfacepotential of the metal structural section 160, causing the potentialwell to become deeper. In addition, the ceramic layer 162 has spikyand/or porous features that increase the area that air molecules caninteract with the molecules at the solid surface, further enhancing heatexchange between solid and air molecules. In some examples, the thinceramic layer 162 can have a thickness of 10 μm. The solid-air heatexchange coefficient of the heat exchange structure 164 can be as muchas five times greater than the solid-air heat exchange coefficient ofthe metal structural section 160 alone.

Experiments were conducted using a light source including twelveone-watt LEDs that were mounted on a planar heat exchange structure 164having an area of 3×3 inch². The heat exchange structure 164 was formedusing an aluminum substrate 160 and thin ceramic layers 162 made ofcarbon, silicon oxide, alumina, boron oxide, titanium nitride, andhafnium oxide. The layer 162 includes spiky micro- and nano-structuresand porous micro- and nano-structures. When all of the twelve 1-wattLEDs were turned on, in an open air environment having a temperaturebetween about 23 to 28 degree C., without using a fan, the hottest spoton the heat exchange structure 164 had a temperature not greater than 62degrees C. The LEDs were powered on for 6 weeks without significantdegradation in light output.

In some examples, the LEDs can be glued to the heat exchange structure164. The LEDs can also be soldered onto bonding pads or signal linesmade from a copper sheet that is glued to the heat exchange structure164.

Experiments were conducted using a light source including a twenty-wattlight module having LEDs, each LED rated about 0.75 watts and mounted ona heat exchange structure having air ducts, such as shown in FIG. 1. Theheat exchange structure has dimensions of about 2-inch by 3-inch by 8.2mm. The walls of the air ducts were 1.6 mm thick, and the cross sectionof the air duct has a square shape with dimension of about 5 mm-by-5 mm.Each air duct has four fins, each fin having a width of about 2 mm andprotruding from one of four walls of the air duct. The heat exchangestructure was formed using an extruded aluminum alloy (Al 6061), whichwas coated with a thin ceramic layer (having a thickness of about 20microns) made of carbon, silicon oxide, alumina, boron oxide, titaniumnitride, and hafnium oxide (e.g., see 162 of FIG. 5A). The thin ceramiclayer includes spiky micro- and nano-structures and porous micro- andnano-structures.

When the light module was turned on with a power less than 15 watts, inan open air environment without using a fan, the hottest spot on theheat exchange structure had a temperature not greater than 60 degrees C.The LEDs were powered on for 10 weeks without significant degradation inlight output. When the light module was turned on with a power of 20watts, in an open air environment having a temperature between about 23to 28 degree C., without using a fan, the hottest spot on the heatexchange structure had a temperature not greater than 75 degrees C. TheLEDs were powered on for 8 weeks without significant degradation inlight output.

Efficient heat dissipation is important for LEDs because the outputpower of the LEDs often degrade as temperature increases. When thetemperature reaches a critical temperature, in some examples above 130degrees C., the LEDs output may drop to near zero. The heat exchangestructure 164 allows heat to be effectively dissipated away from theLEDs, so that the LEDs have higher outputs (i.e., brighter) and longerlifetimes.

The heat exchange structure 164 of FIG. 5A not only has a bettersolid-air heat exchange efficiency, it also has a better solid-liquidheat exchange efficiency. The transfer of heat from the solid to aliquid, and the transfer of heat from the liquid to the solid, can beenhanced by the thin ceramic coating 162.

The heat exchange structure 164 can dissipate heat into the ambient airfaster than by using the metal structural section 160 alone. If theambient air has a temperature higher than the solid, heat transfer fromthe ambient air to the heat exchange structure 164 will also be faster.In other words, the heat exchange structure 164 will absorb heat fromambient air faster than the metal structural section 160 alone.

Applications of Heat Exchange Structures

The following are examples of lighting devices that include high powerLEDs and heat exchange structures that use air ducts and thin ceramiccoatings on the structural sections.

FIG. 10A is an exploded diagram of an automobile fog lamp 220 that canbe mounted on a vehicle. The fog lamp 220 includes an array of highpower LEDs 222 coupled to a heat exchange structure 228. In someexamples, the heat exchange structure 228 has a thin coating of ceramicmaterial, similar to that shown in FIG. 5A. As discussed earlier, thethin coating of ceramic material improves the heat exchange efficiencyof the heat exchange structure 228. The heat exchange structure 228 hasair ducts 224 to create an air pumping effect to move air faster formore efficient heat exchange.

The heat exchange structure 228 can be made by a two-step process.First, a metal or metal alloy is used to form a structure havingexterior wall(s) for mounting the LEDs 222 and interior walls fordefining the air ducts. Second a thin layer of ceramic material isformed on the surface of the structure using a plating process.

In some examples, the fog lamp 220 is mounted on a vehicle such that theair ducts 224 are oriented substantially vertically. The use of thincoating of ceramic material and air ducts allow heat to be dissipatedefficiently when the vehicle is not moving. When the vehicle is moving,an airflow scoop 226 directs air towards lower openings of the air ducts224, increasing the airflow and further enhancing heat dissipation.

The fog lamp 220 includes a front window 230, a glass lens 232 to focusthe light from the array of LEDs 222, a support 234 for supporting theglass lens 232, and a base cover 236. The glass lens 232 can be, forexample, a Fresnel lens. O-rings 238 are provided to prevent moistureand dust from entering the fog lamp 220. Screws 240 are used to fastenthe components of the fog lamp 220 together.

FIG. 10B shows electronic circuit devices 242 that are mounted to anouter surface of the heat exchange structure 228. The devices 242control the operation of the LEDs, for example, regulating thebrightness of the LEDs.

FIG. 10C is an assembled view of the automobile fog lamp 220. The foglamp design can be applied to the head lamps and daylight running lampsfor automobiles, provided that the size and wattage of the LEDs areadjusted accordingly.

FIG. 11A is an exploded diagram of a front-emitting light source 250.The light source 250 can be designed to conform to standard sizes, suchas MR-16 size. The light source 250 includes a light housing 258 andseveral LED modules 254 that have dimensions configured to fit in thelight housing 258. Each LED module 254 includes LEDs 252 that arecoupled to a heat exchange structure 256. In some examples, the surfaceof the heat exchange structure 256 has a thin layer of ceramic materialto improve heat exchange efficiency. The heat exchange structure 256 hasair ducts to enhance air flow. The LEDs 252 are positioned near theopenings at one end of the air ducts.

The modules 254 are fastened together using screws 260 and nuts 262. Themodules 254 are fastened to the light housing 258 using screws 264.Electrical circuits 268 are mounted on the side walls of the heatexchange structures 256 for controlling the LEDs. Electric power isprovided to the LEDs 252 and the electrical circuits 268 through wires266.

FIG. 11B shows an example of the LED modules 254 in which heat generatedby LEDs 252 are carried away by adjacent air ducts 253. In someexamples, holes 255 may be formed on the side walls of the air ducts 253to allow cold air to flow into the air ducts 253 and/or to allow hot airto flow out of the air ducts 253. The electronic components forelectrical circuits 268 are positioned between the heat exchangestructures 256 and act as spacers to facilitate air flow.

FIG. 11C is an assembled view of the light source 250. In some examples,the light source 250 is oriented so that the LEDs 252 face a downwarddirection. Cool air enters the air duct openings near the LEDs 252 andexchanges heat with the air duct walls. Hot air exits through openingsat the other end of the air ducts. The light source design can bemodified to have different sizes and shapes.

FIG. 12A is an exploded diagram of a side-emitting light source 270. Thelight source 270 can be designed to conform to standard sizes, such asthe MR-16 size. The light source 270 includes a holding frame 272 forsupporting six LED modules 276. Each LED module 276 includes LEDs 278coupled to a heat exchange structure 280. In some examples, the heatexchange structure 280 is coated with a thin layer of ceramic materialto increase the heat exchange efficiency. The heat exchange structure256 has air ducts 286 (see FIG. 12B) to enhance air flow.

In the example of FIG. 12A, the holding frame 272 has six legs, such as274 a and 274 b, collectively 274. The legs 274 have elongated groovesfor receiving the sides of LED modules 276. For example, an LED module276 has sides that are received by the grooves of the legs 274 a and 274b. Wires 292 connect the light source 270 to an electric power source.An adapting structure 293 couples the wires 292 to signals lines (notshown) attached to the holding frame 272 for distributing the electricpower to the LED modules 276.

In each LED module 276, the LEDs 278 are mounted on a side wall of theheat exchange structure 280 facing outwards when the light source 270 isassembled (see FIG. 12B). Electronic circuit devices 282 are mounted ona side wall of the heat exchange structure 280 facing inwards when thelight source 270 is assembled.

In some examples, holes can be drilled in the walls of the heat exchangestructure 280 to allow cold air to enter and hot air to exit the airducts.

FIG. 12B is an assembled view of the light source 270. The size of thelight source can be different from MR-16. The light source can have, forexample, three legs, four legs, eight legs, etc., to form differentshapes.

FIG. 13A is an exploded diagram of a wall wash light 294. The wall washlight 294 includes LEDs 296 that are coupled to a heat exchangestructure 298. In some examples, the heat exchange structure 298 iscoated with a thin layer of ceramic material to enhance the heatexchange efficiency. The heat exchange structure 298 has air ducts 300to enhance air flow.

The wall wash light 294 includes a front window 302, a glass lens 304 tofocus the light from the array of LEDs 296, a support 306 for supportingthe glass lens 304, and a base cover 308. O-rings 310 are provided toprevent moisture and dust from entering the wall wash light 294. Thereare two water-tight chambers in the wall wash light 294. The front-sidewater-tight chamber encloses the LEDs 296, and a back-side water-tightchamber encloses a power supply and control circuits for controlling theLEDs 296. Holes are provided at the edges of the heat exchange structure298 (where there are no air ducts) to connect the front-side chamber tothe back-side chamber, to allow signal lines to connect the LEDs 296 tothe power supply and control circuits. The holes for passing the signallines only connect the two water-tight chambers, and are not connectedto the air ducts 300 or to the outside ambient air. This ensures thatmoisture does not enter the front and back chambers. Screws 312 and nuts314 are used to fasten the components of the wall wash light 294together. As shown in FIG. 13B, electrical circuit devices 316 (such asthe power supply and control circuits) are mounted on a side wall of theheat exchange structure 298.

FIG. 13C shows an assembled view of the wall wash light 294. This designhas an advantage of providing a water-tight environment for the LEDs,and at the same time providing effective heat dissipation. This designcan also be used in street lighting lamps.

In some application, the electrical circuit devices 316 (FIG. 13B) canbe mounted on the same side as the LEDs and located in the water-tightenvironment, so that the electrical circuit devices 316 are protectedfrom moisture. Various modifications can be made to these designs. Thewall wash light may include LEDs having different colors, and a controlcircuit may be used to control the overall color and brightness of thewall wash light 294.

Alternative Examples

The description above uses a metal structural section as an example todescribe the useful properties of a heat exchange structure coated witha thin layer of material that modifies the surface potential of the heatexchange structure. The thin coating can also be applied to other typesof structural sections to enhance heat exchange efficiency.

For example, referring to FIG. 8, a heat exchange structure 200 includesa ceramic structural section 202 and a thin layer of ceramic material204 coated on each side of the structural section 202. The ceramicstructural section 202 can be made of aluminum oxide, aluminum nitride,titanium oxide, titanium nitride, zirconium oxide, and zirconiumnitride. The thin layers 204 can be made of silicon oxide, alumina,boron oxide, hafnium oxide, titanium oxide, titanium nitride, zirconiumoxide, and zirconium nitride. The ceramic structural section 202 canhave a layered structure (e.g., having layers on top of other layers) ora non-layered structure. The thin layers 204 can have spiky micro-and/or nano-structures.

Experiments were conducted using a light source including twelveone-watt LEDs that were mounted on a planar heat exchange structure 200(FIG. 8) having a ceramic structural section. The heat exchangestructure 200 has an area of 3×3 inch². The heat exchange structure 200includes a ceramic structural section 202 and a thin layer of ceramicmaterial 204 coated on one side of the structural section 202. Thestructural section 202 was made of aluminum oxide ceramic, and each ofthe thin layers 204 was made of silicon oxide, alumina, boron oxide, andhafnium oxide. The thin layers 204 have spiky micro- andnano-structures. When all of the twelve 1-watt LEDs were turned on, inan open air environment having a temperature between about 23 to 28degree C., without using a fan, the hottest spot on the heat exchangestructure 200 had a temperature not greater than 87° C.

Co-pending U.S. patent application Ser. No. 10/828,154, filed on Oct.20, 2004, titled “Ceramic Composite,” provides description of certainapplications of thin coatings, for example, to provide a flat surface.The contents of U.S. patent application Ser. No. 10/828,154 areincorporated by reference.

The coating process used to coat the ceramic layers onto ceramicstructural sections to generate the heat exchange structure 200 issimilar to that described in U.S. patent application Ser. No.10/828,154. The material compositions used to in the coating process canbe fine tuned (e.g., by adjusting the percentages of each componentmaterial) such that the thin ceramic layer 204 has about 15% more spikeson the surface (as compared to the ceramic layer described in U.S.patent application Ser. No. 10/828,154). The coating process can beadjusted, such as varying the temperature as a function of time, so asto enhance the spiky structures.

The metal structural section 160 in FIG. 5A can be replaced by astructural section made of a composite material, such as fiberreinforced aluminum. In FIGS. 1, 3, and 4, the air ducts 102 do notnecessarily have to be aligned along the same direction. For example, toreduce the overall height of the heat exchange structure 100, 130, or140, the air ducts may be tilted at an angle relative to the verticaldirection, and different air ducts may be tilted towards differentdirections and/or at different angles.

The heat exchange structures can be designed to be used with aparticular type of gas for carrying away heat. The process for coatingthe thin ceramic layer 162 on the metal structural section 160 can beadjusted such that the sub-layer 168 has a porous structure that is atleast partially permeable to the particular type of gas molecules.

Similarly, the heat exchange structures can be designed to be used witha particular type of liquid for carrying away heat. The process forcoating the thin ceramic layer 162 on the metal structural section 160can be adjusted such that the sub-layer 168 has a porous structure thatis at least partially permeable to the particular type of liquidmolecules.

In some examples, the first sub-layer 166 may have cracks or fissuresthat may allow gas molecules to pass. In general, the first sub-layer166 is substantially impermeable to gas molecules relative to the secondsub-layer 168.

The light sources shown in FIGS. 10A, 11A, 12A, and 13A can havedifferent configurations, such as having different sizes and shapes. TheLEDs can be replaced by other types of light emitting devices. The heatexchange structures (e.g., 228 in FIG. 10A, 254 in FIG. 11A, 276 in FIG.12A, and 298 in FIG. 13A) can be made of a ceramic structural sectionthat is coated with a thin layer of ceramic material. In some examples,heat pipes are incorporated to enhance the heat transport and heatdissipation. In some examples, having the air ducts is sufficient forheat dissipation, then the heat exchange structure can be made of ametal or a metal alloy. In some examples, having a thin coating ofceramic material on the heat exchange structure is sufficient for heatdissipation, and air ducts are not used.

Referring to FIG. 9, an example of a heat exchange structure 320includes a heat exchange unit 322 that has air ducts 324, in which onewall of the air duct 324 has a slit 326. The heat exchange unit 322 hasa structural section made of metal, such as aluminum, having a highthermal conductivity. The metal structural section is coated with a thinceramic layer to enhance heat exchange between the heat exchangestructure 320 and the ambient air. The thin ceramic layer is coated ontothe metal structural section using a micro-arc-oxidation platingprocess. The slit 326 facilitates the process of coating the thinceramic layer on the metal structural section. During the platingprocess, the slit 326 allows the chemicals for forming the thin ceramiclayer to be easily coated onto the air duct walls. After the thinceramic layer is coated to the metal structural section, a thin sheet ofmetal plate 328 having holes 330 is attached to the heat exchange unit322. Cold ambient air can flow through the holes 330 and the slit 326into the air duct 324. Similarly, hot air can flow out of the air duct324 through the slit 326 and holes 330.

The heat exchange structure 130 of FIG. 3 can be modified such that theheat exchange unit 134 has air ducts 120, in which each air duct has awall with a slit. A metal plate having holes can be attached to the heatexchange unit 134, similar to the example shown in FIG. 9. In this case,the heat exchange units 134 and the heat pipe 132 can be fabricated fromone piece of metal by using an extrusion process, and the metal platecan be a separate piece of metal.

The air ducts do not have to be straight. The walls of the air ducts canbe curved, such that the air duct follows a curved path. The crosssections of the air ducts do not have to be uniform throughout thelength of the air ducts.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the appended claims. Other examples are within the scopeof the following claims.

1. A method comprising: receiving thermal energy from heat generators at an exterior heat exchange surface of a heat exchange structure, the heat exchange structure comprising a plurality of elongated air ducts, the heat generators positioned along an elongated direction of the air ducts; transferring a portion of the thermal energy from the exterior heat exchange surface to interior heat exchange surfaces of the heat exchange structure, the interior heat exchange surfaces being in the air ducts; and dissipating heat from the interior heat exchange surfaces to air flowing in the air ducts to cause the heated air to rise due to buoyancy of the heated air; wherein dissipating heat from the interior heat exchange surfaces to air flowing in the air ducts further comprises: transferring thermal energy from the interior heat exchange surfaces to an air-impermeable first surface of a thin layer of ceramic material formed on the interior heat exchange surfaces of the heat exchange structure; transferring thermal energy through the thin layer of ceramic material from the air-impermeable first surface of the thin layer of ceramic material to a porous second surface of the thin layer of ceramic material; wherein the porous second surface is exposed to the air flowing in the air ducts; heating air molecules trapped in pores of the porous second surface of the thin layer of ceramic material; and transferring thermal energy from the thin layer of ceramic material to the air flowing in the air ducts by moving the air molecules from the pores of the porous second surface of the thin layer of ceramic material to the air flowing in the air ducts.
 2. The method of claim 1, wherein transferring thermal energy from the heat generators to the interior heat exchange surfaces comprises direct transfer of heat that avoids thermal transfer through a printed-circuit board (PCB).
 3. The method of claim 1, further comprising injecting compressed air into an opening of the air duct.
 4. The method of claim 1 in which the heat generators comprise electronic devices.
 5. A method comprising: transferring, through a heat pipe, thermal energy from a heat generator to a heat exchange structure that comprises a plurality of elongated air ducts, a portion of the heat pipe contacting the heat exchange structure being aligned along an elongated direction of the air ducts; and transferring thermal energy from the heat exchange structure to ambient air flowing in the plurality of air ducts; wherein transferring thermal energy from the heat exchange structure to ambient air flowing in the plurality of air ducts further comprises: transferring thermal energy from the heat pipe to an air-impermeable first surface of a thin layer of ceramic material formed on the heat exchange structure; transferring thermal energy through the thin layer of ceramic material from the air-impermeable first surface of the thin layer of ceramic material to a porous second surface of the thin layer of ceramic material; wherein the porous second surface is exposed to the ambient air flowing in the plurality of air ducts and the air-impermeable first surface of the thin layer of ceramic material is not exposed to the ambient air flowing in the plurality of air ducts; heating air molecules trapped in pores of the porous second surface of the thin layer of ceramic material; and transferring thermal energy from the thin layer of ceramic material to the ambient air flowing in the plurality of air ducts by moving the air molecules from the pores of the porous second surface of the thin layer of ceramic material to the ambient air flowing in the plurality of air ducts.
 6. The method of claim 5, further comprising transferring thermal energy from heated vapor or liquid in the heat pipe to the ambient air in the air ducts through a wall having a thickness less than 5 mm.
 7. A method comprising: fabricating a heat exchange structure and a housing of a heat pipe using one piece of metal, the heat exchange structure comprising a plurality of air ducts and heat exchange surfaces in the air ducts, the heat exchange surfaces configured to exchange heat with air flowing in the air ducts to enhance air flow in the air ducts due to buoyancy of heated air; coating the heat exchange surfaces in the air ducts with a thin layer of ceramic material; wherein coating the heat exchange surfaces further comprises initially coating the heat exchange surfaces with a first sub-layer and finally coating the interior heat exchange surfaces with a second sub-layer; wherein the thin layer of ceramic material is configured to be air impermeable at a first surface of the first sub-layer which attaches to the heat exchange surfaces, and porous at a second surface of the second sub-layer, the second surface being opposed to the first surface and exposed to the air flowing in the air ducts.
 8. The method of claim 7, further comprising the thin layer of ceramic material having a thickness less than 100 μm. 